DESCRIPTION: This proposal will investigate the use of Pro1.5, a monoclonal antibody to the novel human prostate antigen PCTA-1, as a potential immunotherapeutic agent for the treatment of human prostate cancer. The PCTA- 1 antigen is a member of the S-type lectin (i.e., galectin) family, other members of which are involved in cell-cell adhesion, extravasation, and metastatic spread. PCTA-1 appears to be specific for primary and metastatic prostate carcinoma and prostate intraepithelial neoplasia (PIN), but is not expressed by either normal prostate tissue or benign prostate hypertrophy (BPH). In preliminary studies, the PCTA-1-specific monoclonal antibody, Pro 1.5, has been shown to induce regression and complete remission of a well- established human prostate cancer line grown as xenografts in athymic nude mice. This proposal will attempt to 1) validate the utility of the Pro 1.5 monoclonal antibody as a therapeutic agent for treating prostate cancer, and 2) define the mechanism of action for the biological effects of this antibody.